This section provides background information related to the present disclosure which is not necessarily prior art.
FIG. 1 is a view illustrating an example of a lamp employing light emitting diodes, in which a lighting system 100 has a rectifier 110, a regulator 120, and a lamp portion 130 including a plurality of serially connected light emitting diodes A and B. An applied power undergoes a rectifying and smoothing operation before it is fed to the plurality of serially connected light emitting diodes A and B.
FIG. 2 is a view illustrating an example of a serial connection of light emitting diodes, in which a substrate 200 (e.g. a sapphire substrate), a light emitting part or light emitting diode A, and a light emitting part or light emitting diode B are provided. Each of the light emitting parts A and B includes an n-type semiconductor layer 210 (e.g. GaN), an active layer 220 (e.g. InGaN), a p-type semiconductor layer 230 (e.g. GaN). The p-type semiconductor layer 230 is provided with p-side electrodes 240, and the n-type semiconductor layer is provided with n-side electrodes 250. For a serial connection of the light emitting parts A and B, a metal layer 270, running across the top of a dielectric layer 280, connects the p-side electrode 240 of the light emitting part A and the n-side electrode 250 of the light emitting part B.
FIG. 3 is a view illustrating another example of a serial connection of light emitting diodes, in which a package or lamp 300 has a light emitting part A, a light emitting part B, a phosphor film 310 applied onto the light emitting parts A and B, and a lens 320 formed over the phosphor film 310. The light emitting part A and the light emitting part B can be connected in series by means of a wire 330, and they can be electrically connected to outside by means of wires 340 and 350. Additional wires 330 may be required to connect those light emitting parts A and B having the same configuration together.
FIG. 4 is a view illustrating yet another example of a serial connection of light emitting diodes, in which an integrated monolithic light emitting diode chip 400 includes a substrate 493, and light emitting parts A, B and C that are serially connected over the substrate 493. The light emitting parts A, B and C each have an n-type semiconductor layer 410, an active layer 420, and a p-type semiconductor layer 430, but they do not have an insulating substrate 200 as in the light emitting diode of FIG. 2. An n-side pad 440, a conductive layer 491, a deposited metal film 470, and a p-side pad 450 are all involved in the serial connection of the light emitting parts A, B and C. Among other elements that are not yet explained, reference numeral 480 denotes a dielectric layer, and reference numeral 492 denotes a reflective film for reflecting light generated in the active layer 420. However, producing such a monolithic light emitting diode chip 400 constructed as above encounter several disadvantages, that is to say, a number of processes are needed to serially connecting those light emitting parts A, B and C, a problem in any of the light emitting parts may cause a problem for the entire monolithic light emitting diode chip 400, the manufacturing process is difficult, the reliability of the process is not ensured, and so on.